This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. SPECIFIC AIMS: 1. Collect initial data on the cardiovascular, subjective, and reinforcing effects of methamphetamine during treatment with modafinil methamphetamine-dependent subjects. Based on results of prior trials that assessed the safety and efficacy of modafinil for cocaine dependence [Dackis, 2003 #3188;Dackis, 2005 #3869], we anticipate no adverse interaction (such as an enhancement of the cardiovascular effects of methamphetamine), and predict that modafinil will reduce the subjective and reinforcing effects of methamphetamine. 2. Determine whether modafinil (both in the absence and presence of methamphetamine) improves cognitive functioning, especially related to inhibitory control. Chronic abuse is associated with poor response inhibition and other neurocognitive deficits related to executive function (e.g., Kalechstein 2003a). Prior reports suggest that modafinil improves similar cognitive deficits in other clinical populations (e.g., Turner 2004a). Participants will undergo behavioral tests throughout the trial to monitor both acute effects of the drug on cognitive measures of inhibitory control, as well as effects during brief chronic dosing. We anticipate that modafinil administration will be associated with improved performance on tests of inhibitory control.